Strengthen animation listener iteration patterns #7566
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This patch aligns the iteration patterns used by animations and ChangeNotifier. They now both respect re-entrant removal of listeners and coalesce duplication registrations. (Also, ChangeNotifier notification is no longer N^2). This patch introduces ObserverList to avoid the performance regression that the previous version of this patch caused. Fixes flutter#7533
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Attempt 2 |
Hixie
reviewed
Jan 20, 2017
| assert(_debugAssertNotDisposed); | ||
| if (_listeners != null) { | ||
| List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners); | ||
| final List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners); |
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it's tempting to suggest we should do a copy-on-write during iteration here, since we now control this more closely.
but that's probably a premature optimisation.
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Yeah, I'd prefer to wait to see this show up on a profile.
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Please file a bug (or comment on an existing bug) or add a TODO about adding documentation about the fact that you'll get called a surprising number of times if you remove yourself while iterating but you added yourself to multiple listenables that all ended up deferring to the same change notifier. |
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I filed #7570 so we don't lose track of it. |
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This patch aligns the iteration patterns used by animations and
ChangeNotifier. They now both respect re-entrant removal of listeners
and coalesce duplication registrations. (Also, ChangeNotifier
notification is no longer N^2).
This patch introduces ObserverList to avoid the performance regression that the
previous version of this patch caused.
Fixes #7533